Global climate change, often simply referred to as “global warming,” is a complex and scientifically controversial issue that attributes an increase in the average annual surface temperature of Earth to increased concentrations of carbon dioxide and other gases in the atmosphere (air surrounding Earth). Many scientists disagree on how to best interpret data related to climate change.

Scientists also argue about which data (for example, measurements of changes of thickness in arctic ice, measurements of sea temperatures at critical locations, or measurements of certain chemicals in the atmosphere, etc.) should be used to make informed decisions about the extent and rate of global climate change.

Climate describes the long-term conditions or average weather for a region. Throughout Earth’s history, there have been dramatic and cyclic changes (changes that repeat themselves in cycles that can last from thousands to millions of years) in climatic weather patterns corresponding to cycles where glaciers of ice advance and retreat over the landscape.

These glacial cycles occur on the scale of 100,000 years. However, within these larger glacial cycles are shorter duration warming and cooling trends that last from 20,000 to 40,000 years.

Scientists estimate that approximately 10,000 years have elapsed since the end of the last ice age, and examination of physical and biological evidence establishes that since the end of the last ice age there have been fluctuating periods of global warming and cooling.

Concerns over global warming

Global warming actually describes only one of several components involved in climate change and specifically refers to a warming of Earth’s surface outside of the range of normal fluctuations that have occurred throughout Earth’s history.

global temperatures are rising

Measurements made of weather and climate trends during the last decades of the twentieth century raised concern that global temperatures are rising not in response to natural cycles, but rather in response to increasing concentrations of atmospheric gases that are critical to the natural and life-enabling greenhouse effect.

The greenhouse effect describes a process wherein infrared radiation (a form of light) from the Sun is reflected off Earth’s surfaces, but then trapped by clouds to warm Earth’s atmosphere and surface (the light is reflected through the atmosphere and back towards Earth’s surface).

Although the greenhouse effect is essential to life on Earth, if changes result in too strong a greenhouse effect, the changes in Earth’s climate could be dramatic and occur much faster than do natural cycles.

Observations collected over the last century indicate that the average land surface temperature increased by 0.8–1.0°F (0.45–0.6°C). The effects of temperature increase, however, cannot be easily identified or measured because an overall increase in Earth’s temperature may actually cause temperatures at certain locations to decrease because of increased cloud cover associated with increased precipitation (the transfer of water as rain, slow, sleet, or hail from the atmosphere to the surface of Earth).

Measurements and estimates of global precipitation and the sea level changes (the height of Earth’s oceans) indicate that precipitation over the world’s landmasses has increased by approximately 1% during the twentieth century.

Further, as predicted by many global warming models, the increases in precipitation were not uniform. High latitude regions (regions far north or south of the equator) tended to experience greater increases in precipitation, while precipitation declined in tropical areas.

threatened by increasing sea level

Measurements and estimates of sea level show increases of 6–8 inches (15–20 centimeters) during the twentieth century. Geologists and meteorologists (scientists who study Earth’s processes, climate, and weather) estimate that approximately 25% of the sea level rise resulted from the melting of mountain glaciers. The remainder of the rise can be accounted for by an increase in the amount of ocean water in response to higher atmospheric temperatures.

Arctic Melting

Reliable information concerning changes in Arctic and Antarctic ice is difficult to obtain and scientists do not always draw the same conclusions from the data. As a result, conflicting information and ideas exist about the causes and state of Arctic and Antarctic melting.

Arctic Melting

Some scientists argue that ice melting could be due to short-term fluctuations in climate or ocean currents. Many more scientists, however, agree that global climate warming is contributing to the loss of polar ice.

Observations and measurements that indicate ice is melting in the Arctic Sea, and in the ice surrounding Antarctica, is supported by submarine based measurements.

Sonar readings (a measuring device that can send out sound signals and measure how long those signals take to travel to objects, bounce back, and return) show that the distance between the surface of the ocean and the bottom of the ice is decreasing and that ice in some areas is 40% thinner than it was just 40 years ago.

Because ice takes up more room than does liquid water, when Arctic ice melts, it does not directly raise the level of the oceans. In contrast, because much of it is over land, melting Antarctic ice can contribute liquid water to the oceans. Along with other factors, melting ice can result in sea level increases that threaten coastal areas with flooding.

Scientists at the National Aeronautics and Space Administration (NASA) use satellites to measure ice cover, and their results also show Arctic ice cover decreasing.

Between 1978 and 2000, half a million square miles (1.3 million square kilometers) of apparently permanent Arctic ice melted away. At that rate of loss, some scientists argue that the permanent ice caps may be in danger of disappearing before the end of the century.

As more ice disappears, it increases the temperature of Arctic waters because, while ice reflects the majority of the Sun’s rays back into space, darker blue ocean waters are capable of absorbing much more heat-generating light from the Sun.

Although the long-term economic consequences may be dire, over the short term, some companies may try to exploit the melting ice to increase shipping through the Arctic sea.

Many potential routes that now require expensive icebreakers offer significantly shorter routes (and thus lower cost routes) between parts of Europe and the Far East when compared to southerly routes through the Panama or Suez canals.

Changes in the normal greenhouse effect

Because the majority of data clearly show that Earth’s temperature has risen over the last century, the key question for scientists is whether increases in global temperature are part of a natural cycle of change or whether human activity is responsible for the changes.

Estimates of greenhouse gases (those gases that contribute to the greenhouse effect) in the atmosphere that existed prior to the nineteenth century (estimates that are made from current measurements of arctic ice) indicate that over the last few million years the concentration of greenhouse gases remained relatively unchanged prior to the European and American industrial revolutions (the time in history, roughly since 1850, when large scale industry and manufacturing that relied on machines powered by gas and oil began).

During the last 150 years, however, increased emissions from internal combustion engines and the use of certain chemicals have increased concentrations of greenhouse gases.

Although most greenhouse gases occur naturally, the evolution of an industrial civilization has significantly increased levels of these naturally occurring gases. Many scientists argue that these increases are responsible for an abnormal amount of global warming.